Big watermark for tiled pages

Question

I want to arrange pages of my presentation in a rectangular array. I want to print on each page (what may be the equivalent of) a watermark which is a portion of a glyph. For this discussion let us say the glyph is a katakana symbol for ka, spread across 6 pages. When I am done, I should have an array of three rows and two columns of pages with print and with a light-gray water mark on each page, so when I step back some distance, I can look at the watermark(s) and make out the symbol for ka which is about two pages high and two pages wide, but centered so that part of the symbol is on all 6 pages.

I suspect I can use a TeX package for watermarking, but I am asking for an example (or pointer to an example: I am a TeX beginner) that someone more adept than I can post that I can adapt. It is my hope that I can for each page issue the same watermark command, using the same scale for the watermark glyph, but using different offsets for each page (which I am willing to input manually). I am willing to compute the offsets myself to account for the physical space I will use in arranging the pages. For this example, suppose I will have one inch vertically between sheet edges as well as one inch horizontally.

If there is a better package for this effect, I am willing to use it, but I am hoping the learning curve will be mild.

Answer 1

I used my method here What are the ways to position things absolutely on the page? for placing the image on the page. I used Bruno's answer at Can \includegraphics be used to change an image color? to employ the decodearray option of \includegraphics to change the image color of the background.

Other than that, I just employed a clipbox of the magnified image on pages 1-6, using a newly created \IG{}{} macro to test for the specified page and if found, apply the associated clip box accordingly.

\documentclass{article}
\usepackage{everypage}
\usepackage{trimclip,xcolor}
\usepackage{lipsum}
% THESE ARE LaTeX DEFAULTS; CAN CHANGE IF NEEDED.
\def\PageTopMargin{1in}
\def\PageLeftMargin{1in}
\newcommand\atxy[3]{%
 \AddEverypageHook{\smash{\hspace*{\dimexpr-\PageLeftMargin-\hoffset+#1\relax}%
  \raisebox{\dimexpr\PageTopMargin+\voffset-#2\relax}{#3}}}}
\newcommand\IG[2]{\ifnum\thepage=#1\relax\clipbox{#2}{%
  \includegraphics[decodearray={0.9 1 .9 1 .9 1},width=25.5in,height=22in]{ka}}\fi}
\atxy{0in}{11in}{\IG{1}{0in 11in 17in 0in}}
\atxy{0in}{11in}{\IG{2}{8.5in 11in 8.5in 0in}}
\atxy{0in}{11in}{\IG{3}{17in 11in 0in 0in}}
\atxy{0in}{11in}{\IG{4}{0in 0in 17in 11in}}
\atxy{0in}{11in}{\IG{5}{8.5in 0in 8.5in 11in}}
\atxy{0in}{11in}{\IG{6}{17in 0in 0in 11in}}
\begin{document}
\lipsum[1-35]
\centering\fboxsep=0pt\fbox{\includegraphics[width=3in]{ka}}
\end{document}

My original "ka" image is this:

---

Both to provide an example that everyone can run, and to remind users that the decodearray parameter may need to vary its format depending on the color model of the image, I make example-image-A the background image here, where the decodearray only requires 2, not 6 parameters.

\documentclass{article}
\usepackage{everypage}
\usepackage{trimclip,xcolor}
\usepackage{lipsum}
% THESE ARE LaTeX DEFAULTS; CAN CHANGE IF NEEDED.
\def\PageTopMargin{1in}
\def\PageLeftMargin{1in}
\newcommand\atxy[3]{%
 \AddEverypageHook{\smash{\hspace*{\dimexpr-\PageLeftMargin-\hoffset+#1\relax}%
  \raisebox{\dimexpr\PageTopMargin+\voffset-#2\relax}{#3}}}}
\newcommand\IG[2]{\ifnum\thepage=#1\relax\clipbox{#2}{%
  \includegraphics[decodearray={0.8 1},width=25.5in,height=22in]{example-image-a.jpg}}\fi}
\atxy{0in}{11in}{\IG{1}{0in 11in 17in 0in}}
\atxy{0in}{11in}{\IG{2}{8.5in 11in 8.5in 0in}}
\atxy{0in}{11in}{\IG{3}{17in 11in 0in 0in}}
\atxy{0in}{11in}{\IG{4}{0in 0in 17in 11in}}
\atxy{0in}{11in}{\IG{5}{8.5in 0in 8.5in 11in}}
\atxy{0in}{11in}{\IG{6}{17in 0in 0in 11in}}
\begin{document}
\lipsum[1-35]
\centering\fboxsep=0pt\fbox{\includegraphics[width=3in]{example-image-a}}
\end{document}